1. Field of the Invention
This invention relates to a device for controlling a headrest used in a treatment equipment and more particular, to a device for controlling tilting of the headrest to maintain such headrest in comfortable agreement with a patient's head on a headrest of a treatment equipment, such as a dental or medical treatment chair.
2. Prior Art
In the prior art, there have been known a number of headrest controlling devices used for treatment chairs and the like. For example, a device as shown in FIG. 1 has a structure such that a support shaft 51 of a headrest 4 is rotatably connected to a backrest 1 by a pivot 11 inside the backrest 1. Another device as shown in FIG. 2 has a support shaft 52 which is fixedly connected to the backrest 1 but the headrest 4 is movably connected by fitting a cam 62 over a cam 72, the cams being adapted to be fitted one over the other, so as to tiltably control the headrest 4 itself. Another device has been proposed and disclosed by the present Applicant in detail in Japanese Utility Model Publication No. 14477/1974, in which a headrest is moved up and down tiltably with respect to the backrest. The devices mentioned above are all intended to improve the functions of headrest in medical and dental treatment.
However, the prior art devices of the kind described above have been developed for the convenience of an operator, namely, from the standpoint exclusively of the operator and no or little consideration has been given to patients. It is generally desirable that medical treatment chairs be designed to be controlled so as to be freely movable in accordance with a change in the position of a patient resting on the chairs and to be held in a specified fixed state during treatment. Accordingly, it is essential that a headrest mounted to such treatment chair function in like manner. Viewed from the point described, the conventional devices of the type described above appear to pose no problem.
However, the problems common to the prior art devices are that because the center of rotation of the cervical vertebrae of a patient is placed in a different position from the center of rotation of the headrest, the head of the patient put on the headrest does not agree in movement with the headrest, which necessarily results in unnatural position on the part of the patient with the tilting of the head of the patient, with the result that the patient cannot be free from uncomfortable feeling. For this reason, the drawbacks described above cannot be ignored in practicing medical treatment. This is particularly important for the treatment of tooth, eye and nose, wherein the head of a patient is tilted and must be held in a specified spine position to undergo treatment.
For example, in FIG. 1, the locus of rotation A described with the center of rotation O" of a headrest 4 as a center is not in agreement with the locus of tilting B described with the center of tilting O of the cervical vertebrae of the head region of the human body as a center and both loci are those described respectively as shown by arrows. Accordingly, when the headrest 4 is tilted and shifted from the state in FIG. 1A to that in FIG. 1B, the head H of a patient P physically slips out of position in the direction of a backrest 1 (in the direction indicated by arrow O), and the patient P feels that his cervical vertebrae are drawn so much more than is required that he feels uncomfortable and finds it necessary to adjust his posture, with the result that an operator tends to be hindered in his smooth treatment activities. The conventional device shown in FIG. 2 works on the same principle and the patient P is not protected against unnecessary sense of oppression given to his cervical vertebrae when he is shifted in position from the state in FIG. 2A to that in FIG. 2B. Also, the device the present Applicant previously proposed was not free from similar problems either.
The problems common to the prior art are due to the fact that corrections and improvements were made exclusively from the convenience for the operator rather than the patients.